The chorion genes of Drosophila melanogaster provide an excellent system for the study of the genetic control of development. Using recombinant DNA techniques, the basic parameters of chorion gene structure, replication and expression will be determined. Knowledge of normal gene function will allow us to analyze the mechanisms responsible for the altered chorion gene expression in specific mutants such as ocelliless, and in new selected mutant strains. One of the most unusual and interesting aspects of the developmental program of the Drosophila chorion genes is the occurance of specific gene amplification during the late stages of egg chamber development. We are particularly interested in studying the molecular mechanisms of this process and in understanding its relationship to mutant phenotypes.